Current-induced scour beneath initially elevated subsea pipelines. (January 2019)

• Record Type: Journal Article
• Authors: Lee, J.Y.; Hardjanto, F.A.; Cossu, R.; Chai, S.; Leong, Z.Q.; Forrest, A.L.
• Is Part Of: Applied ocean research. Volume 82(2019)
• Page Start: 309
• Page End: 324
• Publication Date: 2019-01
• Subjects: Maximum seabed shear stress -- Equilibrium scour depth -- Subsea pipelines -- Initial pipe elevation; Ocean engineering -- Periodicals; 620.416205
• DOI: 10.1016/j.apor.2018.11.011
• Languages: English
• ISSNs: 0141-1187

Abstract

Highlights: New equation for predicting the maximum seabed shear stress beneath the pipe. The likelihood of scour occurring increases with current velocity but decreases with pipe diameter. New equation for predicting the equilibrium scour depth beneath the pipe. Including the upstream seabed shear stress improved the correlation to experimental data. The influence of the Reynolds number is small. Abstract: When a subsea pipeline is laid on an uneven seabed, certain sections may have an initial elevation with respect to the far-field seabed, e o, and thus potentially affecting the on-bottom stability of the pipeline. This paper focuses on quantifying the effects of the upstream dimensionless seabed shear stress, θ ∞, and Reynolds number, Re, on: (1) the maximum dimensionless seabed shear stress beneath the pipe, θ max, to be compared to the critical shear stress in order to determine whether scour would occur and progress towards an equilibrium state; and, (2) the dimensionless equilibrium scour depth beneath the pipe, S eq / D . Using a 2-D Reynolds averaged Navier-Stokes (RANS) approach along with the k-ω Shear Stress Transport (SST) turbulence model, a parametric study involving 243 computational fluid dynamics (CFD) simulations was conducted. The simulation results were used to develop a closed-form equation for the prediction of θ max . Subsequently, experimental measurements of S eq / D have been compiled from published literature, to develop a new closed-form equation for the prediction of S eq / D with a high correlation to the experimental data. In summary, we present two closed-form equations for the prediction of θ max and S eq / D for pipelines with an initial e o / D, which are applicable for both clear-water and live-bed conditions. The effects of θ ∞ and Re have been included, albeit Re having a small influence as compared to the other parameters.